how to create low poly cliff
It's simple, really.
First, you create two cubes, one slightly smaller than the other.



The select the bigger one of them and in edit mode add loop cuts vertically.
Between 24-48 loops should be enough.


Then select one of the edge loops press 'O' to activate proportional editing and then select random falloff.



Switch to top view, click on the respective axis manipulator and drag forward.



Then add 2 horizontal edge loops and repeat the same process with each of the loops. (Adjust it forward and backward as you see fit)


NOTE : Switch between random falloff and smooth falloff if you feel the edges are too jagged.

Then exit edit mode and move the "rough-edged" cube such that it overlaps the smaller cube.


Next, select the smaller cube and and add the Boolean Modifier and set the operation to "Difference", also make sure the Solver is set to "Bmesh" else the poly-flow may not be even and then press "Apply".



You may delete the bigger cube if you have no further use of it. Now, in edit mode, select all the faces you want to make a ledge or road and press "E" to extrude. Extrude till where you want it.


Hope this is the answer you were looking for. :)